1. Technical Field
The present invention relates to a novel chitinase from yam and a gene encoding the chitinase. This chitinase has a strong lytic activity and, thus, is useful as an agent for controlling plant pathogens.
2. Prior Art
A great number of edible or ornamental plants are cultured at present. Generally, such cultivars are weaker against pathogenic fungi and bacteria than wild-type species. Thus, it is necessary to apply large quantities of agricultural chemicals (agents for controlling plant pathogenic fungi or bacteria) for obtaining sufficient yields. As agents for controlling plant pathogenic fungi or bacteria, chemically synthesized agents of heterocyclic aromatic compound type or organic phosphate ester type have been mainly used to date. However, these chemicals not only manifest their effect on pathogenic fungi or bacteria, but they also have an adverse effect on the human body and cause the problem of residual agricultural chemicals.
Chitinase is an enzyme that hydrolyzes chitin. There are known chitinases belonging to family 18 and those belonging to family 19. It is known that chitinases are involved in the plant defense mechanism against pathogenic fungi and bacteria. Plants infected by pathogenic fungi or bacteria protect themselves by producing chitinases and degrading the pathogen with the chitinase. It is expected that, when such chitinases are applied to soils or plant bodies, they would manifest the same effect as that of the chitinases produced in the plant bodies and thus could protect the plants from infection with pathogenic fungi and/or bacteria. Since chitinases are substances produced by organisms, it can be considered that agents for controlling plant pathogens utilizing chitinases are highly safe against the human body and environments.
Several reports have already been made on the use of plant-derived chitinases as agents for controlling plant pathogens. For example, the present inventors have isolated a chitinase belonging to family 18 from yam and revealed that the chitinase exhibits control effect on pathogens such as Pyricularia oryzae (fungus that causes rice blast) (Japanese Unexamined Patent Publication No. 2000-109405).
The finding of a novel plant chitinase will lead to the development of novel agents for controlling plant pathogens. Besides, for efficient production of agents for controlling plant pathogens using the chitinase, it is necessary to isolate the gene encoding the chitinase.